Cross-grove type constant velocity joint

ABSTRACT

Relief portions 1c1, 1c2 are formed at the boundary regions between the guide groove 1a and the inner peripheral surface 1b, and are respectively positioned at the inner side and the inlet side taking a joint center position 0 as a reference. The relief portions 1c1, 1c2 are gradually increased toward the end portions of the guide groove 1a. Groove depths ( θ1, θ2) of the guide groove 1a at the left region and the right region are identical to each other in all cross-sections orthogonal to the groove bottom line L, and the groove depth is the largest (θ2) at the center region including the joint center position 0, and is gradually decreased from the center region toward the both ends. (θ1: θ2&gt;θ1).

BACKGROUND OF THE INVENTION

The present invention relates to a cross-groove type constant velocityjoint used for propeller shaft or drive shaft of automobiles.

A cross-groove type constant velocity joint is such that each of guidegroove of an outer joint member and each of guide groove of an innerjoint member corresponding to each other are slewed in thecircumferential direction opposite to each other, and a torquetransmitting ball is retained and controlled in a track portion at whichthe both guide grooves are crossed, whereby since play between thetorque transmitting balls and guide grooves can be decreased, the jointhas widely been utilized for propeller shafts or drive shafts ofautomobiles where such play is not permitted.

FIGS. 4(a) and 4(b) illustrates an outer joint member 11 of across-groove type constant velocity joint. As shown in FIG. 4(a), guidegrooves 11a slewed with a cross angle γ in one circumferential directionwith respect to an axial line X and guide grooves 11a slewed with across angle γ in the other circumferential direction are alternatelyformed in an inner peripheral surface 11b of the outer joint member 11,FIG. 4(b) is a view showing the guide groove 11a when seeing the samefrom the inner diametrical side. A groove bottom line L is slewed withthe cross angle γ in the circumferential direction. Dotted lines at bothside wall surfaces of the guide groove 11a are contacting lines Cbetween a torque transmitting ball and the guide groove 11a. The leftand right contacting lines C are parallel to the groove bottom line Land equidistant therefrom. However, boundary lines N between the guidegroove 11a and the inner peripheral surface 11b are not parallel to thegroove bottom line L but have an appointed inclination.

FIGS. 5A, 5B and 5C are cross-sectional views each taken along the linesA--A, B--B, and C--C of the guide groove 11a in FIG. 4(b). The A--Across section shown in FIG. 5A is a cross section in the directionorthogonal to the groove bottom line L of the guide groove 11a at theinner side end, the C--C cross section shown in FIG. 5C is a crosssection in the direction orthogonal to the groove bottom line L of theguide groove 11a at the front side end, and the B--B cross section shownin FIG. 5B is a cross section in the direction orthogonal to the groovebottom line L of the guide groove 11a at the joint center position 0. L'shows the perpendicular line connecting the ball center position 0' tothe groove bottom line L, α shows the contacting angle, and X' shows theposition of the axial line X. As shown in the same figure, although thegroove depth (the length of an arc from the groove bottom line L to theboundary line N) of the guide groove 11a is identical between left sideregion and right side region at the joint center position 0 (B--Bcross-section), the difference of the groove depth between left sideregion and right side region is gradually increased from the jointcenter position 0 toward the groove end side, wherein the difference isthe maximum at the groove end (A--A cross section, C--C cross section).Such a construction necessarily results from the guide groove 11a havinga cross angle γ with respect to the axial line X, and the constructionis inherent in cross-groove type constant velocity joints.

Generally, the guide groove 11a of the outer joint member 11 describedabove is formed by grinding, etc. after forging. Conventionally, inthese production processes, the guide groove 11a has been worked so asto secure accuracy at all regions thereof.

Although the groove depth of the guide groove 11a of the outer jointmember 11 is different between the left side region and the right sideregion at positions apart from the joint center position 0, when theguide groove 11a is given torque by the torque transmitting ball, it isthe shallow side of the guide groove 11a that there is a fear of thetorque transmitting ball coming off from the guide groove 11a, and theperformance and durability of joints are determined by the groove depthat a shallow portion. Therefore, it is necessary to secure a groovedepth required in view of design of joint at a shallow side, as aresult, an outside region D of a deep side (see the A--A cross sectionand C--C cross section in FIGS. 5A and 5C) will become a region whichdoes not have any relation to the performance and durability of joints.

However, in the conventional joint, machining to secure accuracy hasbeen carried out even at the above mentioned region D which does notrelate to the performance and durability of the joint. Such machiningcan be said to be a so-called excessive quality machining. Furthermore,a cycle time of machining is increased since the above mentioned regionD is machined, thereby causing the productivity thereof to be decreased.

Therefore, in order to achieve the above mentioned problem, the presentapplicant previously proposed a construction in which the groove depthof the guide groove of the outer joint member is identical between theleft side region and the right side region taking the groove bottom lineof the guide groove as a reference, and is regular at all regions in thelengthwise direction along the groove bottom line of the guide groove(Japanese patent application no. 216725 of 1993).

However, when this kind of constant velocity joint transmits arotational power while taking an operating angle, the load acting on theguide groove is not uniform on all regions in the lengthwise direction,but is the largest at the central region (normal use region) includingthe joint center position and becomes gradually decreased from thecentral region toward both ends. Therefore, with the constructionalready proposed (Japanese patent application no. 216725 of 1993), sincethe groove depth is regular at all regions in the lengthwise direction,there may be a fear that the load capacity of the central region (normaluse region) will become insufficient, depending upon the use conditions.

SUMMARY OF THE INVENTION

It is therefore an object of the invention is to secure a load capacityin normal use region, whereby to maintain good durability whileincreasing the productivity in the production processes of cross-groovetype constant velocity joints.

To achieve the above-mentioned object, the present invention provides aconstruction in which a groove depth of each of guide grooves of anouter joint member is identical between left side region and right sideregion in each of the cross-sections orthogonal to a groove bottom linethereof, and the groove depth is the largest at a central regionincluding a joint center position and is gradually decreased toward bothend sides from the central region.

According to the present invention, in comparison with the conventionaljoints shown in FIGS. 4(a), 4(b), 5A, 5B and 5C, the region for whichthe accuracy is to be secured is further decreased, and it becomes mucheasier to carry out the quality control. Furthermore, since themachining region is decreased, the cycle time of machining is decreased.Still furthermore, since the groove depth of the guide groove is deepestat the center region which becomes the normal use region, the durabilitycan be secured as in the conventional joint shown in FIG. 4 and FIG. 5.(The durability is increased in comparison with the joint according toJapanese patent application no. 216725 of 1993 already filed).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a cross-groove type constantvelocity joint,

FIG. 2 (a) is a perspective view showing an outer joint member, and

FIG. 2(b) is a view showing a guide groove observed from the innerdiametrical side,

FIGS. 3A, 3B, and 3C are cross-sectional views of the guide grooverespectively taken along the lines A--A, B--B and C--C in FIG. 2(b)respectively,

FIG. 4(a) is a perspective view showing an outer joint member of aconventional joint, and

FIG. 4(b) is a view showing a guide groove observed from the innerdiametrical side, and

FIGS. 5A, 5B, and 5C are cross-sectional views of the guide grooverespectively taken along the lines A--A, B--B and C--C in FIG. 4(b).

PREFERRED EMBODIMENT OF THE INVENTION

Hereinafter, a description is given of a preferred embodiment of theinvention.

FIG. 1 illustrates a cross-groove type constant velocity joint for adrive shaft of an automobile. This constant velocity joint comprises anouter joint member 1 provided with a plurality of guide grooves 1a at aninner peripheral surface 1b thereof, an inner joint member 2 providedwith a plurality of guide grooves 2a at an outer peripheral surface 2bthereof, torque transmitting balls 3 disposed in ball tracks formedbetween the guide grooves 1a and the guide grooves 2a, and a cage 4 forretaining the torque transmitting balls 3.

FIGS. 2(a) and 2(b) illustrate the outer joint member 1 of the abovementioned cross-groove type constant velocity joint. The outer jointmember 1 is of cup-shaped having a stem 1e integral therewith. As shownin FIG. 2(a), guide grooves 1a slewed with a cross angle γ in onecircumferential direction with respect to an axial line X and guidegrooves 1a slewed with a cross angle γ in the other circumferentialdirection are alternately formed in the inner peripheral surface 1b ofthe outer joint member 1. FIG. 2(b) is a view showing a guide groove 1aobserved from the inner diametrical side. A groove bottom line L of theguide groove 1a has a cross angle γ in the circumferential directionwith respect to the axial line X. Dotted lines depicted at both thesides of the guide groove 1a are contacting lines C between the torquetransmitting ball 3 and the guide groove 1a. The contacting lines C areparallel to the groove bottom line L and equidistant thereto.

Relief portions 1c1, 1c2 are formed at the boundary regions between theguide groove 1a and the inner peripheral surface 1b, and arerespectively positioned at the inner side and the inlet side taking ajoint center position 0 as a reference. In the guide groove 1a havingthe cross angle γ in the direction shown in FIG. 2(b), the reliefportion 1c1 is formed from the joint center position 0 to the inlet sideend at the boundary region which is the right side in the same figure,and the relief portion 1c2 is formed from the joint center position 0toward the inner side end at the boundary region which is the left sidein the same figure. The relief portions 1c1, 1c2 are gradually increasedtoward the end portions of the guide groove 1a. Furthermore, in theguide groove 1a having the cross angle γ in the direction opposite tothe direction shown in FIG. 2(b), the region where the relief portions1c1, 1c2 are formed is left-right reversed,

FIGS. 3A, 3B, and 3C are cross-sectional views taken along the lineA--A, B--B, and C--C of the guide groove 1a in FIG. 2(b). The A--Across-section is a cross section in the direction orthogonal to thegroove bottom line L of the guide groove 1a at the inner side end, theC--C cross-section is a cross section in the direction orthogonal to thegroove bottom line L of the guide groove 1 at the inlet side end, andthe B--B cross-section is a cross-section in the direction orthogonal tothe groove bottom line L of the guide groove 1a at the joint centerposition 0. L' is a perpendicular line connecting the ball center line0' to the groove bottom line L, α is a contacting angle, and X' showsthe position of the axial line X. As shown in the same figure, groovedepths (θ1, θ2) of the guide groove 1a at the left region and the rightregion are identical to each other in all cross-sections orthogonal tothe groove bottom line L, and the groove depth is the largest (θ2) atthe center region including the joint center position 0, and isgradually decreased from the center region toward the both ends.(θ1:θ2>θ1).

The depths (θ1, θ2) are determined in design by the use conditions ofjoint, load torque, etc. The relief portions 1c1, 1c2 are providedoutside the groove depths (regions) (θ1, θ2) (that is, they correspondto the regions D shown in FIGS. 5A and 5C). Since the regions where therelief portions 1c1, 1c2 are provided is not in relation to theperformance and durability of the joint, no worry arises about alowering of the performance and durability of the joint even thoughrelief portions 1c1, 1c2 are provided in these regions. Furthermore,since it is enough that accuracy of the guide groove 1a is secured atthe groove depths (regions) (θ1, θ2), the region to be secured inaccuracy is decreased in comparison with the conventional joint shown inFIGS. 4(a), 4(b), 5A 5B, and 5C. Still furthermore, when this kind ofconstant velocity joint transmits a rotational power while taking anoperating angle, the center region including the joint center position 0of the guide groove 1a becomes a normal use region, wherein the loadbecomes the largest in this region. Therefore, by the groove depth ofthe guide groove 1a being the largest at this center region, durabilityof the joint can be secured as in the conventional joint shown in FIGS.4(a), 4(b), 5A, 5B, and 5C.

The relief portions 1c1, 1c2 described above may be formedsimultaneously with the guide groove 1a when forging the outer jointmember 1 or may be formed by carrying out another machining afterforging. Various shapes of the relief portions 1c1, 1c2 may beavailable, such as a tapered shape, a shape having curvature, etc. inaddition to a stepped shape shown in FIG. 2 and FIG. 3.

As described above, in the cross-groove type constant velocity joint, bysecuring the groove depths θ1, θ2 (θ2>θ1) of the guide groove 1a of theouter joint member being necessary in view of designing of joints, andmaking the regions outside this groove region be the relief portions1c1, 1c2, it is possible to decrease the region for which the accuracyis to be secured, in the guide grooves 1a in comparison with theconventional joints shown in FIGS. 4(a), 4(b), 5A, 5B, and 5C, wherebyit is possible to attempt to increase the productivity in the jointproduction process.

What is claimed is:
 1. A cross-groove type constant velocity jointcomprising:an outer joint member provided at an inner peripheral surfacethereof with guide grooves slewed in one circumferential direction withrespect to an axial line thereof and guide grooves slewed in the othercircumferential direction alternately; an inner joint member provided atan outer peripheral surface thereof with guide grooves, each of theguide grooves forming a ball track by cooperating with each of the guidegrooves of the outer joint member corresponding thereto, each of theguide grooves slewed in the circumferential direction opposite to thecorresponding guide groove of the outer joint member; a torquetransmitting ball disposed in each of the ball tracks; and a cage forretaining the torque transmitting balls, wherein a groove depth of eachof the guide grooves of the outer joint member is identical between leftside region and right side region in each of the cross-sectionsorthogonal to a groove bottom line thereof, and the groove depth is thelargest at a central region including a joint center position and isgradually decreased toward both end sides from the central region.
 2. Anouter joint member for a cross-groove type constant joint provided at aninner peripheral surface thereof with guide grooves slewed in onecircumferential direction with respect to an axial line thereof andguide grooves slewed in the other circumferential direction alternately,wherein a groove depth of each of the guide grooves is identical betweenleft side region and right side region in each of the cross-sectionsorthogonal to a groove bottom line thereof, and the groove depth is thelargest at a central region including a joint center position and isgradually decreased toward both end sides from the central region.